DE102015218576A1 - ADJUSTMENT CONTROL UNIT - Google Patents

Abstract

A control unit (2) of a hydraulic unit has a control piston (3) which is slidably disposed in a control cylinder (4) to provide hydraulic fluid under servo pressure (P2) to a first outlet (8) of the control unit (2) , which is suitable for adjusting the hydraulic unit. The servo pressure (P2) is proportional to the sum of the internal forces of the hydraulic unit and the operating forces acting on the control unit (2). The hydraulic fluid provided at the outlet (8) is supplied to an inlet (7) of the control unit (2) through a feed pressure feed (P1) to an inlet (7). The control piston (3) has a blind hole (5) in the direction of a longitudinal axis (13) of the control unit (2), wherein in the blind hole (5) a pressure relief valve (20) is arranged, which acts as a pilot unit, and a two-sided pressure relief piston ( 23), which is arranged in the blind hole (5) and relative to the control piston (3) by means of an actuator (6) is displaceable, so that by moving the pressure limiting piston (23) reduces the feed pressure as a hydraulic actuating pressure (P4) both on the medial end face (26) and on the distal end face (27) of the pressure-limiting piston (23) and also on the end faces (12) of the control piston (3) acts. The control piston (3) is displaceable by the sum of the pressure forces generated by the control pressure (P4) and the force of the actuator (6) in the control cylinder (4).

Description

The invention relates to a control unit, comprising a control piston, which is arranged displaceably in a control cylinder in order to allow the transmission of hydraulic fluid under servo pressure to a servo unit for the controlled adjustment of a hydraulic unit. The servo pressure provided at a first outlet of the control unit is proportional to the sum of the internal forces on the control unit and the operating forces acting thereon. In this case, the hydraulic fluid, which is passed to the outlet, passed through a feed pressure supply to an inlet of the control unit, as indicated in the preamble of claim 1.

Such a control unit is, for example, from DE 10 2008 050 835 A1 and DE 101 27 907 A1 known.

Hydraulic units and their components, such as hydrostatic pumps, hydrostatic motors, hydrostatic valves or power cylinders are often operated in potentially explosive environments or areas where there is a risk of explosion. Therefore, they must be designed according to specific guidelines for avoiding explosions. With respect to the electrical devices, this implies that the electrical energy used in the controls must be prevented from causing an explosion, usually, e.g. B. by consuming and costly encapsulation of the same, which simultaneously claimed a large space. In this case, elaborate protective measures are required, such. B. explosion-proof housing for the components. This allows the use of energies high enough to provide sufficiently high control forces for actuation of the valves or other hydraulic control units. Transferred to electrical proportional displacement controls that are widely used, eg. As in variable displacement pumps, this means large-volume housing for the isolation of proportional solenoids and all connected electrical contacts and power lines.

Alternatively, the electrical energy used is reduced so much that potential sparks are too weak to cause an explosion. This case is called "intrinsically safe". However, this alternative has a reduced level of performance for generating control forces. Consequently, such a solution of an explosion-proof design often has the disadvantage that the limited energies are not sufficient to provide forces that are high enough for reliable, high-quality control / adjustment of a hydraulic unit. Furthermore, these relatively low control forces are prone to the superposition of external disturbances that further reduce the quality of the control.

In order to adapt a conventional non-explosion-proof electrical proportional adjustment to an intrinsically safe design, several aspects must be optimized. Due to the low electrical energy that is used to provide actuator forces, the spring forces must be reduced / adjusted to the level of available magnetic forces. In addition, all types of interference must be reduced and / or sufficiently shielded by the control unit so as not to cause interference. A reduction of the mechanical friction and the flow forces must be made. Next inertial forces must also be reduced because they act with or against the magnetic forces, depending on the direction of the adjustment. All these expenses for such a design with low electrical energy would be considerable, but only partially successful.

Another approach to achieve sufficiently high actuation forces for a secure design with low currents is, for example, the use of a hydraulic pilot control or amplifier stage. Such a pilot control or amplification stage is, for example, in DE 34 02 508 A1 described. A hydraulic pilot valve within the control unit of a variable displacement hydraulic machine is also off DE 10 2008 050 835 A1 known. There, the proportional solenoids are relatively highly electrically applied and thus not intrinsically safe. Furthermore, the pilot pressure relief valve is located away from the main proportional adjustment assemblies, which is a bulky system accordingly. Consequently, the above-mentioned solutions of the prior art have the disadvantage that they are relatively bulky and / or not intrinsically safe.

It is therefore an object of the present invention to provide a control unit which uses relatively low actuation forces, e.g. B. low electrical currents. However, sufficiently high adjustment forces are to be generated in order to ensure a high quality of the control of the adjustment of hydraulic units. The control unit according to the invention should furthermore have a small number of components, be robust in terms of design, cost-effective and preferably be integrated into the control unit of hydraulic units. Another object of the present invention is that control units of already existing hydraulic devices against a control unit according to the present invention are easily replaceable or adaptable.

The objects are achieved by a control unit according to claim 1, wherein preferred embodiments are specified in the subclaims, which are directly or indirectly dependent on claim 1.

Accordingly, the control unit according to the preamble of claim 1 of the present invention is based on a generally non-intrinsically safe control unit. Deviating from such a control unit, the control unit according to the invention is characterized in that the control piston has at least at one end face along a blind hole aligned in the longitudinal direction of the control unit. In this blind hole a pressure reducing valve is arranged, which functions as a pilot control unit. For this purpose, a two-sided pressure-reducing piston is arranged, which is displaceable in the longitudinal blind-hole bore relative to the control piston by means of an actuator. By moving the pressure reducing piston relative to the control piston feed pressure as a hydraulic actuating pressure on both end faces of the pressure reducing piston, d. H. on the medial and the distal end face, and directed to the distal end of the control piston. In this case, the control piston in the control cylinder by the sum of the pressure forces, which acts by the control pressure acting on the distal end face of the control piston and on both faces of the pressure-reducing piston, and by the force of the actuator, which in the direction of adjustment of the pressure-reducing piston supportive acts.

The invention provides a solution to the above-mentioned drawbacks of the prior art and is intrinsically safe in the case of the use of electrical energy. It is essential that the force of an electric, hydraulic, pneumatic and / or mechanical actuator is less than the force that is necessary to move the control piston in the control cylinder. Consequently, the relatively low operating forces provided by the actuator are boosted by hydraulic forces provided by the pilot stage according to the invention, in particular by means of the inventive arrangement of a pressure reducing valve within a longitudinal blind bore of the control piston. These reinforcing forces are generated internally in the control unit, preferably in the longitudinal blind hole of the control piston. More preferably, the external configuration of the control piston used in the present invention is that of control pistons used in control units which are known from the prior art and are not intrinsically safe. Inside, the control unit according to the invention deviates from the prior art at least by the features which are specified in the characterizing part of claim 1.

According to the invention, the actuator of the control unit according to the invention does not directly actuate the control piston of the proportional adjustment unit, as is known from conventional control units of the prior art. The actuator according to the invention displaces a pressure reducing piston which is integrated in the control piston and is displaceable relative thereto. The pressure reducing piston acts together with the longitudinal blind hole in the control piston as a pilot valve. If the pressure piston is displaced relative to the control piston, the pressure reducing valve opens a line from the feed pressure supply at the inlet of the control unit via the end faces of the pressure reducing piston to the end face of the control piston. For this purpose, the pressure-reducing piston has a longitudinal bore which connects the distal and the medial end faces of the pressure-reducing piston. On both end faces of the pressure reducing piston pressure chambers are arranged within the blind hole of the control piston, which are acted upon by hydraulic fluid, which is supplied via the feed pressure inlet of the control unit.

The pressure chamber at the distal end of the control piston, into which projects the distal end face of the pressure reducing piston, has a larger diameter. Consequently, the hydraulic force generated in the pressure chamber at the distal end is greater than the hydraulic force in the pressure chamber at the internal, medial end of the pressure reducer piston. Consequently, when pressurized hydraulic fluid is allowed to flow through the longitudinal bore of the pressure reducing piston to both end surfaces, i. H. directed to both pressure chambers, an additional hydraulic force is generated to that of the actuator in the direction of the intended displacement of the control piston. According to the invention, the magnitude of this hydraulic force is determined by the magnitude of the displacement of the pressure reducing piston by the actuator. At the same time, the pilot pressure at the inner end face - the medial end face of the pressure reducer - which is remote from the actuator produces a counterforce hydraulic force against the actuator force which, as noted above, is less than the hydraulic force due to pilot pressure on the distal end End face is generated.

Since the pressure reducing piston according to the invention is acted on both faces with pressurized hydraulic fluid, which preferably comes from supply pressure supply, the effective force for moving the pressure reducing piston depends on the size of the two end faces. In a preferred embodiment of the invention, the pressure-reducing piston has a stepped Execution on, which means that it has two end faces of different sizes. Here, the medial end face of the pressure reducing piston, which is arranged on the side facing away from the actuator, smaller than the distal end face on which the actuator acts directly or indirectly. Consequently, the difference in diameter of the two end faces of the pressure reducing piston affects the amount of counterforce against the actuator - since the pressure level acting on both end faces is the same. Conversely, since the allowable actuator force is limited to avoid explosions in hazardous environments, this defines the size of an annular surface on the pressure piston which effectively generates the hydraulic counterforce against the actuator force. In other words, the difference in the size of the two end faces of the pressure-reducing piston multiplied by the setting pressure plus the mechanical force of the pressure reducing spring must not be greater than the allowable Aktuatorkraft that is available for an intrinsically safe design of the control unit according to the invention.

If the two end faces of the pressure reducing piston were the same size and the same pressure acting on the two end faces, so no hydraulic counterforce would be generated against the Aktuatorkraft and would have to be applied solely by the pressure reducing spring. However, such a pressure reducing spring is provided in the control unit according to the invention for biasing the pressure reducing piston to its closed position in which the hydraulic fluid line is interrupted by the longitudinal bore of the pressure reducing piston and allowing pressure discharge from the medial pressure chambers via an outlet to a lower pressure area. If the actuator were only balanced by elastic forces of the pressure-reducing spring, then these forces would have to be as low as the available Aktuatorkraft. Due to internal forces (friction) during the displacement of the pressure reducing piston, this would not lead to a robust design with a high quality of the control unit according to the invention. Therefore, according to the invention, the effective pressure end faces of the pressure reducing piston are of different sizes. This can be achieved by using a pressure reducing piston with a stepped configuration or by shielding parts of the medial face from the hydraulic setting pressure, for example by a plunger which directs the actuator force to the pressure reducing piston.

Ultimately, the forces acting on the control piston to displace it in the medial direction result from the diameter of the control piston, the control pressure acting thereon plus the force of the actuator on the pressure reducing piston. If the pressure piston is in a bushing design, d. H. as an insert construction within the blind hole of the control piston, then the actuating pressure acts on an end face of the sleeve, whereby this end face forms part of the end face of the control piston.

In a preferred embodiment of the invention, the pressure reducing piston is guided in a pressure reducing valve sleeve which is arranged in the blind bore of the control piston, wherein pressurized hydraulic fluid can be passed via Druckmindernerventilbuchse Druckminderventilbuchse to a low pressure outlet of the control unit in fluid communication with a low pressure region , For example, a tank or the housing of a hydraulic unit is.

The invention makes it possible to adapt electrical proportional control units of the conventional type in order to be able to use (very) small control forces with only minimal changes. Preferably, a control piston according to the invention fits into existing control units. Consequently, an existing embodiment can be easily adapted to the requirements of an intrinsically safe and explosion proof construction. Intrinsic safety is advantageous because it does not require housings or shields of electrical components such as solenoids, power lines, or plugs. In addition, it is easier to use in practice. With its own safe design, it is possible, for example, to open and close electrical contacts without having to turn off the hydraulic unit.

As can be easily understood by a person skilled in the art, the idea according to the invention is applicable not only to electronic displacement control systems for achieving intrinsic safety, but also to systems whose hydraulic, pneumatic, hydromechanical or electrical actuator forces are intended to be amplified without to cause big changes to the control unit. Likewise, a reverse use is included by the inventive idea. In the event that it is desired to reduce the actuating forces, for example by changing the way in which the actuating forces of the control unit are provided, for example by changing the hydraulically generated actuating forces into pneumatically, mechanically or manually generated forces. As one skilled in the art will appreciate, the inventive idea is not limited to control units intended for use in an explosive environment. In the following the invention with further details with the aid of a preferred embodiment and with reference to the accompanying drawings is explained in more detail. Show it:

1 shows a partial sectional view of an embodiment of a control unit according to the invention in a first operating state;

2 shows a partial cross-sectional view of a control unit according to the invention in a second operating state;

3 a cross section of a symmetrical control unit according to the invention in a second operating state.

1 shows a partial cross-sectional view of an embodiment of a control unit 2 according to the invention. Shown is the right side of a generally symmetrical control unit 2 that is a conventional control cylinder 4 in which a movable and generally symmetrical control piston 3 is arranged, as in 3 is shown. The control piston 3 in the 1 to 3 is shown as an example is used for adjustment of hydraulic units, for example. Hydrostatic pumps or motors with reversible hydraulic fluid flow.

In the 1 shown right side of a control unit 2 shows the right half of a control piston 3 , which slidably in a control cylinder 4 is guided. An intrinsically safe actuator 6 acts exclusively and indirectly on the spool 3 by means of a pestle 17 , The displacement of the control piston 3 opens or closes certain lines for hydraulic fluid to adjust the adjustment of the hydraulic unit. These connections are controlled by control edges 15 . 16 passing through an annular groove 10 by machine into the outer surface of the control piston 3 are introduced, opened or closed. Hydraulic fluid is, for example. Through a feed pump (not shown) with feed pressure P ₁ an inlet 7 that in the steering cylinder 4 is arranged, supplied and may as a servo pressure P ₂ to an outlet 8th be directed. The pressure level of the servo pressure P ₂ is proportional to the displacement of the control piston 3 relative to the control cylinder 4 , Another outlet 9 leads to a region of low pressure which corresponds to a pressure P ₃ and is generally referred to as a sump, tank or housing. These features and the general operation of a control unit are known to those skilled in the art, so that it can be dispensed with further details.

The control unit 2 according to 1 differs from conventional control units in that they are a hydraulic precursor or a pilot unit in the form of a pressure reducing valve 20 having, slidably in a longitudinal blind hole 5 of the control piston 3 is arranged. The blind hole 5 is along the longitudinal direction 13 the control unit 2 aligned. The pressure reducing valve 20 has a pressure reducing valve piston 23 on that in a socket 21 is arranged, which axially fixed in the blind hole 5 of the control piston 3 is attached. An end face of the bush 21 laying on the floor 11 the blind hole 5 at. This face of the socket 21 is, for example, with an end cap 19 closed, which also as an attachment for a pressure reducing valve spring 28 serves. A radial bore 14 extends from the control piston 23 over the socket 21 to the control piston 3 and connects the inlet 7 for feed pressure P ₁ with a longitudinal bore 24 in the socket 21 , The pressure reducer piston 23 is slidable in the hole 24 arranged.

The pressure reducer piston 23 is designed, for example, stepped, ie it has a first, distal end face 26 and a second medial end 27 with different diameters. The distal end surface 26 is the smaller of the two end faces 26 . 27 and is to the pestle 17 of the actuator 6 directed. tappet 17 only touches the pressure reducing piston 23 , and only on the distal end 26 , tappet 17 can on the pressure reducer piston 23 along the longitudinal axis 13 the control unit 2 act and medially directed forces on the distal face 26 exercise. The pressure reducer piston 23 also has a through hole 25 on that from the distal end face 26 to the medial face 27 leads. At the medial end face 27 has the through hole 25 an enlarged diameter to a pressure reducing spring 28 to pick up the pressure reducer piston 23 in the direction of the pestle 17 biases. Radial holes 34 in the pressure-reducing piston 23 fluidly connect a remote peripheral area 38 on the pressure reducer piston 23 with the through hole 25 , The area 38 can with the radial bore 35 in the socket 21 overlap that to the outlet 9 leads, which is connected to a region of low pressure. This overlap depends on the relative position of the pressure reducer piston 23 in the socket 21 and occurs when the pressure reducer piston 23 is in the closed position. In case of overlapping the recessed area 38 and the radial bore 35 becomes a fluid connection between the through hole 25 and the second outlet 9 produced on housing pressure P ₃ . This is described below in more detail.

The peripheral surface 29 of the pressure-reducing piston 23 is stepped, causing different diameters of the medial face 26 and the distal end surface 27 be achieved. At the same time they define an annular surface 30 in the overlapping area of the two diameters. A corresponding ring shoulder 39 is located in the longitudinal bore 24 the socket 21 so that the ring surface 30 at the ring shoulder 39 can strike and so the distal stroke of the pressure reducer piston 23 relative to the socket 21 and to the control piston 3 in the socket 21 is fixed, can limit.

At the distal end of the pressure reducer piston 23 near the distal end face 26 there is a groove 31 on the outer surface of the pressure reducer piston 23 and defines a control pressure control edge 33 , The groove 31 can be in an overlapping position with the radial bore 14 in the socket 21 be brought, with the inlet 7 fluidic with the groove 31 is connected. When such an overlap occurs, hydraulic fluid is removed from the inlet 7 over the radial bore 14 that the control piston 3 and the socket 21 interspersed, to a distal pressure chamber 36 in the longitudinal blind hole 5 of the control piston 3 directed by a flange 18 is closed. In the pressure chamber 36 can hydraulic fluid under actuating pressure P ₄ on the front page 12 of the control piston 3 , on the free end face 22 the socket 21 and forwarded along the groove 31 , on the distal end face 26 of the pressure-reducing piston 23 Act. The level of the pressure level of the control pressure P ₄ is adjusted by the height of the displacement of the pressure-reducing piston 23 with respect to the control piston 3 , The larger the displacement of the pressure reducing piston 23 relative to the socket 21 , the higher the control pressure P ₄ in the distal pressure chamber 36 and in the areas that communicate directly with it, for example, the through-hole 25 in the pressure-reducing piston 23 and the medial pressure chamber 37 , By means of through-hole 25 is set pressure P ₄ from the distal chamber 36 to the medial pressure chamber 37 passed between the medial end 27 of the pressure-reducing piston 23 and the end cap 19 the socket 21 is arranged. Consequently, the control pressure P ₄ also acts on the medial end face 27 of the pressure-reducing piston 23 ,

The operating state of the control unit 2 , in the 1 is shown, the pilot stage or gain (boost) of the control forces for adjusting the hydraulic unit inactive. In this state, the ring area touch each other 30 the socket 21 and the annular shoulder 39 of the pressure-reducing piston 23 , Consequently, the pressure-reducing piston is located 23 in its completely distal position. In this inactive position, the control edge overlaps 33 for signal pressure not with the radial bore 14 , Consequently, hydraulic fluid can not leak from the radial bore 14 via the signal pressure groove 31 to the distal pressure chamber 36 flow. In this closed position of the pressure reducing valve 20 is the distal pressure chamber 36 over the through hole 25 , the radial holes 34 and 35 and via the signal pressure relief groove 32 to the outlet 9 relaxed, which is connected to a region of low pressure, for example. Housing pressure P _3rd Consequently, in both pressure chambers 36 and 37 Low pressure at pressure level P ₃ available. Consequently, the control pressure P4 in this inactive state of the control unit according to the invention 2 substantially equal to the low pressure level P ₃ . Furthermore, the servo pressure P _{2 is} not affected because the control edge 15 not with the inlet 7 for system pressure P ₁ overlaps.

2 shows a sectional view of a left side of a control unit 2 according to the invention in a second, active operating state. In this operating state, the pilot stage or the boost of the control forces on the control piston 3 on this side of the control unit 2 active. Because the control unit 2 is formed symmetrically, the same reference numerals, in 1 were used for corresponding features in 2 and consequently also in 3 used.

In 2 pushes the actuator 6 the pestle 17 active against the first face 26 of the pressure-reducing piston 23 , The pressure reducer piston 23 becomes in the medial direction against the force of a biasing spring 28 postponed. This causes overlapping of the groove 31 with the radial bore 14 , which hydraulic fluid under system pressure P ₁ leads. Consequently, the hydraulic pressure in the pressure chamber increases 36 and generates a set pressure level P ₄ in the pressure chamber 36 , which by feed pressure P ₁ , at the inlet 7 is fed, is fed. Simultaneously with the overlapping of the groove 31 with the radial bore 14 becomes the overlap of the excluded area 38 and the radial bore 35 dissolved, so that the pressure level in the pressure chamber 36 not over the low pressure outlet 9 can be relaxed. However, the pressure level P ₄ in the pressure chambers 36 and 37 over the through hole 25 in the pressure-reducing piston 23 connected with each other. Consequently, the pressure in the pressure chamber corresponds 37 the signal pressure P ₄ in the pressure chamber 36 and acts on the medial end 27 of the pressure-reducing piston 23 ,

The displacement of the pressure-reducing piston 23 also closes the flow channel for hydraulic fluid from the through-hole 25 over the radial bores 34 and 35 to Druckentspannungsnut 32 that leads as the area 38 with reduced outside diameter of the bush 21 is defined. The pressure relief groove 32 in turn is with the second outlet 9 on housing pressure P ₃ . Since this fluid channel is closed, pressure P ₄ acts on the medial end face 27 of the pressure-reducing piston 23 , On the distal end 26 of the pressure-reducing piston 23 the same actuating pressure P ₄ acts on the distal end face 26 as well as on the front 22 the socket 21 and on the remaining ring face 12 of the control piston 3 ,

According to the operating condition of the 2 is the effective force acting in the medial direction on the control piston 3 acts, given by the sum of the hydraulic forces caused by the control pressure P ₄ on the front page 12 of the control piston 3 . on the face area 22 the socket 21 and on the face 26 of the pressure-reducing piston 23 be generated, ie the entire cross-sectional area of the pressure chamber 36 plus the mechanical force of the actuator 6 on the pestle 17 , In the distal direction, the forces are given by the product of the area of the medial end face 27 of the pressure-reducing piston 23 multiplied by the setting pressure P ₄ plus the force of the pressure reducing spring 28 , Since the sum of the pressure-sensitive areas in the medial area is smaller than the sum of the pressure-sensitive areas in the distal area, the resulting force is in the direction of the center of the control unit 2 directed and pushes the spool to the right, indicating in 3 is shown.

The force on the control piston 3 acts, is triggered by the force of the actuator 6 that on the pressure reducer piston 23 acts whose displacement the hydraulic forces on the control piston 3 cause. The role of the actuator 6 is essentially limited to the pressure reducer piston 23 in the socket 21 to move. The generated value of the control pressure P ₄ is proportional to the size of the displacement of the pressure-reducing piston 23 relative to the control piston 3 , Consequently, the force generated by the actuator 6 is generated, which is preferably an electromagnet, significantly enhanced by the controlled supply of hydraulic pressure to the end faces of the control piston 3 , This allows the use of relatively low actuator forces, which require low electrical power when an intrinsically safe solenoid is used.

3 shows a section of a complete control unit 2 According to the invention in the active operating state of 2 , The symmetrical control piston 3 is shifted to the right, as in 2 shown by the spacing of the dotted lines representing the respective axes of symmetry of the control piston 3 and the control cylinder 4 represent is shown. This shift causes the inlet to overlap 7 for hydraulic fluid under feed pressure P ₁ with a through the control edge 15 limited area 10 with reduced diameter on the control piston 3 , Consequently, hydraulic fluid will be from the right inlet 7 to the first right outlet 8th under servo pressure P _{2 passed} whose pressure level - as usual - is determined by the amount of displacement of the control edge 15 of the control piston 3 relative to the control cylinder 4 ,

Although the preferred embodiment disclosed in the 1 to 3 is shown in detail, the person skilled in the art recognizes that the scope of the inventive idea is not limited to this embodiment. In the embodiment shown, the socket 21 , the cap 19 , the pressure reducer 23 and the pressure reducing spring 28 axially fixed as a preassembled module 20 , ie as a preassembled pressure reducing valve 20 , in the blind hole 5 of the control piston 3 be fixed. Nevertheless, a person skilled in the art will easily find a way, at least parts of the pressure reducing valve 20 in the control piston 3 integrate while reducing the number of parts. Consequently, all embodiments are also encompassed by the inventive idea, which is a pressure reducing valve 20 for generating an additional hydraulic force on the control piston 3 used, which is caused by the Aktuatorkraft for controlled adjustment of a hydraulic unit. Here, the use of feed pressure P _{1 is} not limited to a pressure feed, which is generated by a feed pump. Generally speaking, the boost pressure used may be any pressure in a hydraulic unit that is higher than the ambient pressure to generate a boosting effect in the sense of the present invention.

Needless to say, any other type of actuator can be used for the invention instead of the proportional electromagnet, which uses low currents. Thus, switching electromagnets are also included in the idea of the invention, which open up the possibility of switchable hydraulic controls, which put possibly proportional controls of hydraulic units out of operation. Also, the use of operating switchable valves utilizing pneumatic, hydromechanical, mechanical, etc. actuator forces to initiate the enhancement effect of the invention is within the scope of the invention.

As mentioned above, the inventive idea is not limited to hydrostatic machines such as hydrostatic pumps or motors. The inventive idea is also applicable to all types of hydraulic units, such as hydraulic cylinders, e.g. B. applicable for the movement of loads.

LIST OF REFERENCE NUMBERS

2

control unit

3

spool

4

control cylinder

5

Blind hole

6

actuator

7

Inlet (feed pressure)

8th

first outlet (servo pressure)

9

second outlet (low pressure)

10

ring groove

11

Bottom blind hole

12

Face control spool

13

longitudinal axis

14

radial bore

15

Control edge for servo printing

16

Control edge for pressure limitation

17

tappet

18

flange

19

End cap bushing

20

Pressure relief valve

21

Pressure relief bushing

22

free end face of the bush

23

Pressure limiting piston

24

longitudinal bore

25

Through Hole

26

medial face

27

distal end face

28

Pressure relief spring

29

Side area / surface

30

ring surface

31

Groove for signal pressure

32

Stelldruckbegrenzungsnut

33

control edge

34

Radial bore piston

35

Radial bore bush

36

distal pressure chamber

37

medial pressure chamber

38

exempt area

39

shoulder

P ₁

supply pressure

P ₂

servo pressure

P ₃

casing pressure

P ₄

Control pressure / control pressure

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008050835 A1 [0002, 0006]
• DE 10127907 A1 [0002]
• DE 3402508 A1 [0006]

Claims (11)

Control unit ( 2 ) a hydraulic unit having a control piston ( 3 ), which is displaceable in a control cylinder ( 4 ) is arranged to a hydraulic fluid under servo pressure (P ₂ ) at a first outlet ( 8th ) of the control unit ( 2 ) which is adapted to displace the hydraulic unit, wherein the servo pressure (P ₂ ) is proportional to a sum of the internal forces of the hydraulic unit and the operating forces applied to the control unit ( 2 ), wherein the hydraulic fluid at the outlet ( 8th ) by a feed pressure supply with feed pressure (P ₁ ) to an inlet ( 7 ) of the control unit ( 2 ), characterized in that the control piston ( 3 ) a blind hole ( 5 ) in the direction of a longitudinal axis ( 13 ) of the control unit ( 2 ), in which blind hole ( 5 ) a pressure relief valve ( 20 ), which acts as a pilot control unit, and a double-sided pressure limiting piston ( 23 ), which in the blind hole ( 5 ) and relative to the control piston ( 3 ) by an actuator ( 6 ) is displaceable, so that by moving the pressure limiting piston ( 23 ) reduced feed pressure as hydraulic actuating pressure (P ₄ ) on both, the medial end face ( 26 ) as well as the distal end face ( 27 ) of the pressure limiting piston ( 23 ) and on the front surfaces ( 12 ) of the control piston ( 3 ), wherein the control piston ( 3 ) by the sum of the pressure forces that can be generated by the control pressure (P ₄ ), and the force of the actuator ( 6 ) is displaceable. Control unit ( 2 ) according to claim 1, characterized in that the actuator ( 6 ) is a proportional magnet on the distal end face ( 27 ) of the pressure limiting piston ( 23 ) acts. Control unit ( 2 ) according to claim (2), characterized in that the actuator ( 6 ) is intrinsically safe in terms of explosion safety. Control unit ( 2 ) according to one of the preceding claims, characterized in that the force of the actuator ( 6 ) is less than the force necessary to move the control piston ( 3 ) in the control cylinder ( 4 ) to move. Control unit ( 2 ) according to one of the preceding claims, characterized in that the pressure limiting piston ( 23 ) by a pressure limiting spring ( 28 ), which are on the second, medial end face ( 26 ) of the pressure limiting piston ( 23 ) acts, is biased and held in a starting position. Control unit ( 2 ) According to one of the preceding claims, characterized in that a lateral surface ( 29 ) of the pressure limiting piston ( 23 ) via a radial bore ( 14 ) in the control piston ( 3 ) in fluid communication with an inlet ( 7 ) for hydraulic fluid under feed pressure (P ₁ ) and that hydraulic fluid to the distal end face ( 27 ) of the pressure limiting piston ( 23 ) via a signal pressure groove ( 31 ) in the lateral surface ( 29 ) is conductive. Control unit ( 2 ) according to one of the preceding claims, characterized in that the pressure limiting piston ( 23 ) a through hole ( 25 ) in the direction of the longitudinal axis ( 13 ) of the control unit ( 2 ), through which through-bore ( 25 ) Hydraulic fluid from the distal end surface ( 27 ) to the medial end face ( 26 ) of the pressure limiting piston ( 23 ) is conductive. Control unit ( 2 ) according to one of the preceding claims, characterized in that the pressure limiting piston ( 23 ) in a pressure limiting bushing ( 21 ) is guided in the blind hole ( 5 ) of the control piston ( 3 ) is arranged, wherein hydraulic fluid under control pressure (P ₄ ) via Stelldruckbegrenzungsnuten ( 32 ) in the pressure limiting bushing ( 21 ) to a second outlet ( 9 ) of the control unit ( 2 ) which is in fluid communication with a region of low pressure. Control unit ( 2 ) according to claim 8, characterized in that the pressure limiting piston ( 23 ) a radial bore ( 35 ), with which through-bore ( 35 ) Hydraulic fluid from the through-bore ( 25 ) to the second outlet ( 9 ) is conductive. Control unit ( 2 ) according to one of the preceding claims, characterized in that the pressure limiting piston ( 23 ) has two regions of different diameter, the medial end surface ( 26 ), the distal end face ( 27 ) and a ring surface ( 30 ) in a region which connects the regions of the different diameters, can be acted on by actuating pressure (P ₄ ) and the annular surface ( 30 ) permanently with the output ( 9 ) is in fluid communication. Control device ( 2 ) according to claim 10, characterized in that the medial end face ( 26 ) the larger end face of the pressure limiting piston ( 23 ).

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